Electron tube amplification system



Patented Aug. 20, 1940 TE ST T PATENT OFFICE ELECTRON TUBE AMPL F c-ATION SYSTEM Walter Seller, Cincinnati, Ohio, assignor of onehalf to William H. 'Woodin, Jr., Tucson, Ariz.

Original application September 25, 1934, Serial Divided and this application November 18, 1938, Serial N0. 241-,265

4 Claims. (Cl. 1.79-17 1) This application is'a divisionof my application Serial Number 745,460 filed September 25, 1934, I

for Electron tube amplification system, now patent. 2,138,891, granted December 6, 1938.

One of the objects of my invention is to provide an electron tube amplification system employing multiple electrode electron tubes in which the electrodes are interconnected by balanced circuits for insuring stabilized operation of the amplification system. 7

Another object of my invention is to provide a circuit arrangement for insuring balanced operation. of a resistance coupled electron tube amplification system for efiecting maximum amplification per stage without interference from para- 1 si-tic oscillations. a I I Still another object of my invention is t o-pro vide, a resistance coupled electron tube amplification system in which opposing. potentials are introducedin selected portions of the resistance coupled amplifier circuit for preventing oscillation'while allowing maximum amplification.

A further object of my invention is to provide an electron tube amplification system having circuits interconnecting the electrodes of the electron tubes including a resistor carrying current of-one electron tube element, the potential drop across which is balanced by the sum of a drop of potential across a resistor carrying part or all of the current of the total supply power, and another voltage produced bythe drop in potential acrossa resistor carrying the current of any other element of the same tube.

A still further object of my invention is to provide an electron tube amplification system in .which balanced operation is obtained by balancing the potential drops in elements connected withthe electrodesof an electron tube to a substantially balanced condition and then introducas set forth'more' fully in the specification'hereinafter following by reference to the accompanying drawing which diagrammatically illustrates the amplification circuit of my invention.

Referring to the drawing in detail, I have. il-

lustrated my invention by a circuit arrangement for a two-stage electron tube amplifier, butI desire that it be understood that the principles. of

my invention are applicable to multistage amplifiers'generally in which a common power supply circuit is provided for all of the: electron tubes,

in theamplification system.

In this. arrangement tubes 33 andv 34' are shownwith the output circuit of one. tube coupled with the input'circui-t-of the succeeding tube and having an input circuit 35-and an output circuit 36.-

The'power supplyof direct current characteristicv is connected at 31 and traverses the series path. 38, which path. contains resistors 39, 4i ,v 4l-',"4=2., 43 and 44. Tube 331inoludes heater element 33a,. cathode. 3317,. grid 33c, grid 33d andplate 336.

Similarly, electron tube 34 contains heater eleresistor 40. The anode potential for: anode 336 is determined by the drop across resistors 40- and M. The output circuit of tube 33 is coupled with the input circuit of tube 34 through resistor 45.

The bias on control grid 340 is determined by the j drop across resistor 42-. The potential on grid 34d is derived from the drop acrossresistor 43-. The balancing potential on grid 34d is determined by the drop across resistors 46 and 41 7 connected in series with tap 48 intermediate resistors 43 and 44. The potential on anode 34a is determined by resistor 49' connected with point 5B in the series power supply circuit 38. The output circuit of the amplifier at 36 connects at point 5] intermediate resistors 46 and 41 in circuit with grid 34d and the point 52' in the output circuit of tube. All of the stages of the amplifier are balanced in the last stage. This is possible because a common power supply circuit is provided for all of the stages.

The resistance network and the connections to the electrodes in tube 34, as above described, may be. considered as a balanced bridge arrangement in which: resistance 44- constitutes one leg; re-;

sistance 49,; a second leg; the internal resistance between cathode 34b and anode 34a of the. tube,

the third leg; and resistance 43, the fourth leg.

This fourth leg is modified to include the internal resistance between the cathode 34b and the grid 34d of the tube 34 and resistance elements 46 and 4? connected in series, the series circuit being connected in parallel with the resistance 43. The source of potential for the bridge is connected at point 50 between resistances 44 and 49 and to the cathode 34b. The output is taken from the opposite terminals of the bridge, viz., 5| and 52. The modification of the fourth leg of the bridge which includes resistance 4'! permits the resistance 4'1 to be included also in the output circuit. The potential drop across resistance 41, or some equivalent voltage, is a necessary factor in the balancing of the bridge circuit.

The condition of balance of the bridge is the condition of zero voltage across the output terminals. Consider the potential drop across resistance 4'! as E, the resistances 49 and 44 as R1 and R0, respectively, and the currents in R1 and R as I1 and I0, respectively. The factors affecting the balance of the bridge are the currents I0 and I1. These currents are each dependent on a common factor, which is the source of potential of the system, and the effects thereof may be made to neutralize each other for any variations in the potential source by properly adjusting the resistance of the circuit.

It will be appreciated that the same principles are involved in both a direct heated cathode circuit, device, and the indirect cathode heating system as long as all power is obtained from the same source. There isv a simultaneous change in the heating of the cathode, and the plate potential under conditions of changes in the common power supply. Accordingly, variation in cathode emission due to variation of power supply in the circuit shown in my invention will be :balanced similar to the direct heated system.

Now for the circuit to be balanced for a change Io in I0 and a corresponding change I1 in I1, the following equation must hold:

Ro(I0-|AI0) +E'=R1(I1+AI1) Substituting for R1 from (1) RoUo-l-Alo) +E=(RoIo+E) (I1+AI1)/I1 Cancelling and rearranging:

RoU1AI'o-IOAI1)=+EAI1 The above is the value of R0 for balanced conditions in terms of E, I1, I0 and the slope of the I1 vs. Io characteristics. R1 is then determined by Equation 1. I6

constant and it can be considered as a first approximation as constant, because the effect on it of a change in electron emission is counteracted by the effect on it of the change in potential drop across resistance 43 caused by a simultaneous change in Io, it is evident that the characteristics must be such that the denominator is a constant for all values of In in order that Re can be a constant. By putting the denominator in differential form equating it to a constant and solving the differential equation, we obtain the characteristics of I1 vs. Io necessary to have Re a constant as follows:

1.0g (I -]C1)=10g I1+10g 762 10g (I k )=10g 76211 Equation (5) is the general equation of a straight line. Therefore, if the portion of the characteristics near the operating value of In is straight, the circuit will balance and remain balanced.

The length of this straight portion determines the range of external fluctuations that can be balanced. This requirement is usually fulfilled for normal operating conditions. This one-tube circuit affords so simple a means of balancing external tube variations that it is as easily set up as an unbalanced circuit, will operate much more satisfactorily, and with refinements, will balance as closely as the two-tube circuit. The advantages over the two-tube circuit are: the elimination of the difiiculty in balancing, of extra apparatus, and of the necessity of obtaining exactly similar tubes, which are not readily procurable.

The balancing in these circuits is accomplished by adjusting resistances R0, R1, and voltage E. Without voltage E, the circuit would not balance even though it appears the drop R0 I0 could be made to balance drop R1 I1. This is not possible, as can be seen, by allowing E to equal zero in the first equation after Equation 2, which will then cause R0 to cancel out of the equation and thereby eliminate the means of adjusting for balance. To have a voltage drop E in the circuit R0, R1, and the output, is an essential feature of the circuit of my invention.

The actual values of the resistances R0 and R1 need not be calculated from Equations 3 and 1,but can be determined experimentally as follows: A suitable D. 0. electric current meter is placed across the output terminals with R0 not far from the expected correct value and R1 is adjusted until the meter reads zero. The supply current is then increased by increasing the voltage into the supply circuit and the deflection of the meter noted. Then, with a new value of R0 (a value which differs from the expected correct value in the opposite direction from that of the first value taken), R1 is again adjusted for zero reading of the meter, and the deflection of the meter again noted for an increase in supply current. If the correct value of R0 for balance is near the value which was expected, this second deflection will be in the opposite direction to the first. Values of R0 between these two are then taken and the above procedure repeated until a value of R0 and R1 is found for which no defiection is produced in the meter when-thesupply current is changed. Every tube even of thesame type and make differs enough in characteristics to require the values of Rb and R1 tobe determined experimentally for balance against supply power changes.

The assumption that E is constant is introduced to simplify the discussion and to show the' fundamental idea of balancing against changes in supply power.

Actually, the assumption of E being constant is an unnecessary assumption The following discussion will show that the circuit of my invention will balance not approximately, but completely for normal operating voltageson the tube and that the conditions are not altered from those just given, 4! being any suitable constant resistance, and R0 and R1 oletermine experimentally in exactly the same way as before. Call resistance, R2; and the current through it, I2. Then, for balance at some current In with the corresponding currents I1 and 12, the following equation must hold:

Now to remain balanced when Io changes to Io-I-Alo causing I2 to change to Iz+AI2 and I1 to Ii-j-Ali, the following equation must hold also:

R0(IO+AIO) +R2I2+R2AI2=R1(I1+AI1) substituting R0 in this, gives R R 1 A Cancelling and rearranging, gives R1(I1AI0I0AI1) =R2(I2AIo-I0A1g) This is a similar" condition to that of the pre- A vious case, the denominator having exactly the same form. Here, the numerator also has exactly the same form. In order for the denomithat must fit the requirement of the characteristics of the tube given by Equation 7, the resistance R2 can be chosen arbitrarily within the operating range and R0 and R1 determined experimentally in exactly the same Way as indicated in the sim- --plified discussion.

If, in place of solving first for R0 in Equation 6, R1 is obtained as follows:

and then it 'is'eliminated in place of R0, the second condition of balance,

AI FZ IQ I1XT; Rf A1 I 2I IE is obtained;

From this, it is seen that Re can just as well be chosen arbitrarily in place of R2 and then R2 and R1 adjusted for the balance condition experimentally in exactly the same way as R0 and R1 were. This is a more convenient method of adjusting, as during adjustment, the tube can be held closer to its operating voltages. As R0 is arbitrary, a special case of this circuit is when R0=0.

So far, it has been shown that these circuits will completely balance out changes in the supply power sources. It will be shown now that a further adjustment of the circuit of my invention is possible, whereby the circuit will balance both changes in the power source, and changes in cathode emission due not only to variations in the power supply, but to any cause as, for example,

- the deterioration of the cathode or filament. It

is preferable to have the grid 3401 to which resistances 46 and 41 are connected, between the cathode and the control grid for this type of balancing; Let changes in the electron emission not due to power supply variations produce changes of A'Iz and A'Ii in I2 and I1 respectively. For these changes, there will be no change in Io; i. e., AIo=U.

For balancing at currents I0, I1 and I2, we have Then for balance after a change A'Iz and A'Il when 10 does not change,

ELAE

Equations 8, 9, and 10 are the three conditions that must be fulfilled for this balance.

Let the slopes V o, "2,K/T

Then by substituting these values in Equations 8, 9, and 10 and eliminating the his we obtain I1' la-1mg) -F I0 I I1'7Lg the condition between the currents and slopes that must be fulfilled.

The circuit of my invention embraces any method of'changing the characteristics of a tube, as for example, by placing a resistance across the tube, so that'it canbe balanced. My invention is not confined to electron tubes, but is also applicable to any form of cathode ray tubes.

My invention contemplates any amplification system of one or more electron tubes having three or more elements in which all elements of each tube are supplied by one source of electric power and in which. the drop in potential across a resistor carrying the current of one element can be balanced by the sum of a drop of potential across a resistor carrying part or all of the total I have described my invention in a certain pre- '5 1 sistors in the power supply paths.

ferred embodiment but I desire that it be understood that modifications may be made without departing from the spirit of my invention. For example, I have mentioned the arrangement of re- I may employ impedances in the power supply paths in lieu of resistors. Other changes may be made in the circuits of my invention and I intend no limitations upon my invention other than imposed by the scope of the appended claims.

What I claim as new and desire to secure by Letters Patent of the United States is as follows:

1. A multistage electron tube amplification system including a plurality of electron tube devices, anode, cathode and grid electrodes in each of said electron tube devices, a source of power common to said plurality of electron tube devices, and a balanced output circuit connected with the electron tube device in the last stage of said amplification system comprising a connection from one terminal of said source of power to the anode in said last stage electron tube device, a resistance element in said connection, a series circuit including a plurality of resistance elements connected to said source of power, a connection from the cathode in said last stage electron tube device to a point in said series circuit intermediate two of said plurality of resistors, a grid elec- :trode in said last stage electron tube device connected to a point in said series circuit thence through another of said plurality of resistance elements to the terminal of said source of power connected to said anode, a separate resistance .element in said connection to said grid, and output terminals connected to said anode and said separate resistance element, the potentials of said output terminals being balanced by the algebraic sum of the potential drops across the said resistance elements connected between said anode and said source of power and between said grid electrode and said source of power.

2. A multistage electron tube amplification system including a plurality of electron tube devices, anode, cathode and grid electrodes in each of said electron tube devices, a source of power common to said plurality of electron tube devices, and a balanced output circuit connected with the electron tube device in the last stage of said amplification system comprising a connection from one terminal of said source of power to the anode through another of said plurality of impedance in said last stage electron tube device, an impedance element in said connection, a series circuit including a plurality of impedance elements con- 1 nected to said source of power, a connection from "the cathode in said last stage electron tube device to a point in said series circuit intermediate two of said plurality of impedances, a grid electrode in said last stage electron tube device connected to a point in said series circuit thence elements to the terminal of said source of power connected to said anode, a separate impedance element in said connection to said grid, and output terminals connected to said anode and said 3. A multistage electron tube amplification system including a plurality of electron tube devices, anode, cathode and grid electrodes in each of said electron tube devices, a source of power common to said plurality of electron tube devices, and a balanced output circuit connected with the electron tube device in the last stage of said amplification system comprising a connection from one terminal of said source of power to the anode in said last stage electron tube device, an impedance element in said connection, a series circuit including a plurality of impedance elements connected to said source of power, a connection from the cathode of the electron tube device in the last stage of said electron tube amplification system to a point in series circuit intermediate two of said plurality of impedance elements, a grid electrode in the electron tube in the last stage of said amplification system connected to a point in said series circuit, thence through another of said plurality of impedance elements to the terminal of said source of power connected to said anode, a separate impedance element in said connection to said grid, output terminals connected to said anode and said separate impedance element, the potentials of said output terminals being balanced by the algebraic sum of the potential drops across the said impedance elements connected between said anode and said source of power and between said grid electrode and said source of power, and a resistance element constituting coupling means between the output circuit of one electron tube and the input circuit of said last mentioned electron tube.

4. A multistage electron tube amplification system including a plurality of electron tube devices, anode, cathode and grid electrodes in each of said electron tube devices, a source of power common to said plurality of electron tube devices, and a balanced output circuit connected with the electron tube device in the last stage of said amplification system comprising a connection from one terminal of said source of power to the anode in said last stage electron tube device, an impedance element in said connection, a series circuit including a plurality of impedance elements connected to said sourcev of power, a connection from the cathode of the electron tube device in the last stage of said electron tube amplification system to a point in series circuit intermediate two of said plurality of impedance elements, a grid electrode in the electron tube in the last stage of said amplification system connected to a point in said series circuit, thence through another of said plurality of impedance elements to the terminal of said source of power connected to said anode, a separate impedance element in said connection to said grid, output terminals connected to said anode and said separate impedance element, the potentials of said output terminals being balanced by the algebraic sum of the potential drops across the said impedance elements connected between said anode and said source of power and between said grid electrode and said source of power, and an impedance element constituting coupling means between the output circuit of one electron tube and and the input circuit of said last mentioned electron tube.

WALTER SOLLER. 

